Naturespeak A naturalist's view of the world

March 9, 2009

Nut-seeking Missiles

Filed under: Uncategorized — wykes @ 9:23 pm

If you only watch them for a short time, Fox Squirrels can appear to be downright stupid.  Their random style of movement and jerky nature paints them with an appealing but buffoonish brush. These nut-munchers are not buffoons, however. Though squirreliness is not considered a positive human trait, it is a positive squirrel trait. Besides, I doubt any self respecting squirrel would ever strive to be humanly. Humans can’t climb trees and jump from limb to limb, they can’t  open a nut with their bare teeth (without permanent dental trauma, that is),  and they can’t remember things like a squirrel can. Yes, that’s right – squirrels have excellent memories. They are, in fact, nut-seeking missiles.

Everyone, well almost everyone, knows that squirrels bury nuts in the fall. The average Kindergartner would likely tell you that “the squirrlies do it so that they can dig them up in the winter for lunch.”  Your average adult Joe would even say that squirrels bury so many nuts that they forget some and that these forgotten seeds eventually become trees. Stupid squirrels plant forests, in other words.  Your average naturalist will continually say that squirrels locate their subterranean nut supplies by using their superior sense of smell alone. Well, as it turns out, those average naturalists – myself included – were  mostly wrong and those average Joes were right, but for the wrong reasons. The little kids were right, but so what, us adults are still the mostest smarter.

The trick to discovering the essentials of squirreliness is to watch them for an extended period of time. I would like you to watch this short video showing a little over a minute in the life of a Fox Squirrel. What you’ll see is a frantic mammal apparently covering a lot of  ground in a fruitless attempt to find buried walnuts. True, she doesn’t find any during the period of filming (this is the edited version) but what is important here is to watch what is really going on. The creature is creeping close to the ground with her head down and nose close to the ground. Indeed she looks like a bloodhound on the trail of a convicted nut.  But rather than taking meticulous sniffs over every inch of ground, she is very quick about it. She dashes about from point to point and then stops to scan the ground with her sniffer. Miss squirrel  is mentally putting herself into global position and then employing her smell to hone in on the target.

Squirrels, such as the Grey and the Fox kind, are scatter horders. They bury their nutty treasures over a wide area so that other nut eaters won’t find them all. They can afford to do this because they can use spatial clues (memory) and smell to re-find them. Scientists put this to the test by burying extra nuts in a plot of ground where a test squirrel had already buried a bunch. The squirrel, when released back onto the plot for some extended nutting time, ended up finding its own nuts twice as often as the new nuts. If this was a random process driven by smell alone, the squirrel would have recovered an equal number of new and old nuts. So, you see, the rodent has a sense of place after all.

If you want to see something really fascinating, take a look at this U-Tube video showing a squirrel memory test. It seems that, in this scenario anyway, the animal was relying exclusively on memory. By continually returning to the same cup position to find the hidden peanuts, this individual was completely overriding the smell game in order to play the shell game.

Other research has shown that squirrels tend to recover over 80-90% of their buried nuts if they remain alive. Squirrels rarely dig exploratory holes because they can pin point their targets with military accuracy. A frequent sight throughout the winter, and during these pre-spring times, is to find shallow excavated holes with a partially exposed walnuts at the bottom (see here).  The reason these nuts were left in place is because the squirrel was able to determine that they had gone bad using their incredible sense of smell. They left them in place without further wasted effort. The squirrel’s got both  nose and navigation knack.

Unfortunately, it is all too customary for squirrels not to remain alive over any given winter, so it is up to other opportunistic invader squirrels to try their luck at sniffing out the abandoned nut supplies. These squirrels, not familiar with the lay of the land, have to resort to smell alone and therefore  can’t find them all. It could be said, therefore, that most of the forgotten nuts aren’t really forgotten after all. They were never known of in the first place!

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